Ok guys. This is a question for my 69 GTO. I recently started having a problem with my tranny. After coming to a full stop, the tranny is not dropping down into first gear. I must now shift into first when taking off from a stop or it will start off in second. It is also shifting later than it should. The shifts are still firm and there is no slippage. What do ya think?

While I'm at it, I am also having a problem with the TH400 in my '37 ******. This one occasionaly slips badly in first when accelerating from a stop. It slips for several seconds before fully engaging. After that it performs normally in all other gears. Any ideas?

 

I have a '71 vette with the same tranny and had about the same problem. Normally, if I was just cruising it would shift at about 2,000 to 2,500 rpm. When it was giving me trouble, it was shifting at about 3,000 to 4,000 rpm which meant it was revved really loud and you had to be going pretty fast to get it to shift. I thought that it could be something majorly wrong but it turned out that it was the vacuum line to the modulator on the tranny. The line was broken on the end which was letting some of the vacuum escape so it wouldn't shift right. I don't know if this will solve your problem but it's worth a try.

 

Tom,
I'm no expert, just a little general knowledge. I looked at my Haynes for the Vette and for the GTO's symptoms they say to check vacuum line & vacuum modulator assembly.

On the ******- they don't address intermitant slippage just in one gear. They say to check fluid level for slippage in all gears, for what that's worth- you've probably done that. A buddy has been to trans school & when I asked him about my Navajo slipping in 1st gear sometimes he said it's probably low line pressure- a typical problem for that trans. I'd try a service on it to see if it fixes it because if the filter is clogged it can cause low line pressure. If not that it could be internal- hopefully not. Good luck on both.

 

Yeah, the GTO's vacuum line was the first thing I checked earlier this week. It is fine. I Serviced the tranny today(new filter & fluid), but it is still doing the same thing. I guess I'll replace the modulator next weekend and see what happens.

Les, I have been having that 1st gear slippage problem every spring in the ******. I figure it gets all gummed up after sitting all winter without use. I change the filter every spring and it solves the problem, but not this time I wonder if the valve body could get gummed up and remain that way after the filter/fluid change?

 

Yep, I'll bet it could get gummed up. I'll also bet that there's some kinda flush made that you could run through there to clean it up. If a filter change has fixed it before it doesn't sound like a serious problem.

On an unrelated note- do you know if Chuck has suffered a blow to the head recently(maybe inflicted by Leslie)??? I'm tryin to understand why he's selling the 69?!?!?!?!

 

On the first one, you have the classic symptoms of a sticking governor. Sometimes a few manual downshifts will unstick it, but not always. It will usually do it again. Happens often just after a rebuild. There are governor filters in the trans that often get left out during rebuilds and the slightest debris will stick.score it. The good news is it's easy to repair/replace. It is under the small cover with 4- 5/16" bolts on the right side rear. Just pull the cover and slip the governor out. No big deal...it isn't timed or anything like that. Now hold it vertical with the gear end upwards. Slowly depress the governor weights "closed" and watch the piston interally slide up and down in the governor bore through one of the oblong slots in the side of housing. It MUST slide easily with just it's own weight. If it sticks at all, it will cause issues. SOMETIMES you can clean them and get them going again, but they are very picky. Sometimes you will find the plastic gear stripped on the end. It can be easily replaced without buying a new governor. If you have to get a new one, try transmission rebuilder suppliers locally. CK yellow pages. The prices are typically very reasonable and they will sell to the public. Usually around $20 or less for a governor. Make sure you get the right one. The WOT shift points are determined by the governor and you need to get the right one for your application. ALL T-400 ones interchange physically, so if you want to change your shift points, you can select one from a higher HP car or get an aftermarket one from B&M etc that come with various weights and springs to fine tune it.

The second one just sounds wounded. I think it's been going away for awhile and you've been able to get by. May need to check in closer on that one.


JIM

 

Jim, Thanks for the detailed instructions. That does not sound too bad at all.

That did not sound as encouraging. Oh well, at least I didn't destroy the case again like the last tranny I ran in that car.


Les, Too many sustained G's in his Z06 may be the cause of the condition you suspect.